System and method for radiation detection and imaging

ABSTRACT

System and method for detecting and imaging radiation. A preferred embodiment comprises a substrate with electronic circuitry to detect changes in a transduction signal, an intermediate conductive layer disposed above and electrically connected to the electronic circuitry, and a lower separation layer with a high coefficient of thermal resistance that partially separates the intermediate conductive layer from the electronic circuitry. The preferred embodiment also includes a top layer disposed above the intermediate conductive layer and an absorptive layer overlying the top layer, with the absorptive layer being electrically connected to the intermediate conductive layer. The absorptive layer produces a transduction signal that is proportional to an amount of radiation incident on the absorptive layer. The vertical fabrication of the radiation sensor allows for sensor arrays with a good fill factor, permitting the creation of sensor arrays with high resolution while maintaining low costs.

TECHNICAL FIELD

The present invention relates generally to a system and a method forintegrated circuits, and more particularly to a system and a method fordetecting and imaging radiation.

BACKGROUND

It is possible to detect radiation, such as infrared (IR) radiation,using one of two general types of sensors. A first sensor type (photonsensor) detects the presence of the radiation by detecting the directinteraction of the radiation with the atomic lattice of the sensingmaterial in the sensor, and a second sensor type (thermal sensor)detects the radiation by detecting a temperature change in the sensordue to the absorbed radiation. The temperature change causes a physicalparameter of the sensor, such as resistance or voltage, to change andtherefore can be detected by electronic circuitry.

With thermal sensors, thermal mass (M_(TH)) and thermal conductivity(C_(TH)) determine the response time of the system, where the responsetime is proportional to M_(TH)/C_(TH). Generally, it is desired to havethe greatest temperature change per unit of radiant power on the sensor,implying a sensor with a small thermal mass and/or a well thermallyisolated sensor. However, if the sensor is too well isolated, the heatwill not dissipate fast enough, therefore extending the response time ofthe thermal sensor.

With reference now to FIGS. 1 a and 1 b, there are shown diagramsillustrating prior art implementations of thermal sensor pixels. Thediagrams shown in FIGS. 1 a and 1 b illustrate two different prior artimplementations of a single pixel in a thermal sensor array. The diagramshown in FIG. 1 a illustrates a single pixel 100 used in the thermalsensor array. The pixel 100 includes a detector (or absorber) 105 thatincludes a pair of legs 110 that elevates the detector 105 from theremainder of the thermal sensor array to thermally isolate the detector105 from other detectors in the thermal sensor array. Conductors 115 and120 couple the detector 105 to electronic circuitry and permit thedetection of changes in physical parameters, such as resistance andvoltage.

The diagram shown in FIG. 1 b illustrates a single pixel 150 used in athermal sensor array. The pixel 150 includes a detector 155 that iscoupled to a rim 160 via serpentines 165. The use of the serpentines 165yields a high coefficient of thermal resistivity due to the smallcross-section of the serpentines 165, which provides electricalconnectivity while minimizing thermal transfer. The pixel 150 can becreated using a bulk etching process, allowing for mass production ofthermal sensor arrays.

One disadvantage of the prior art is that the design of the pixels,although yielding good thermal performance, has a poor fill factor forthe thermal sensor array due to the underlying support structure of thepixels, such as the legs 110, the rim 160, and the serpentines 165,consuming a significant amount of integrated circuit real estate. A lowfill factor results in a thermal sensor array that generally cannot bereadily scaled since a thermal sensor array with a large number ofpixels may be unnecessarily large.

Another disadvantage of the prior art is the design of pixels withsignificant thermal mass, which can increase the response time of thepixels and the thermal sensor array. This can lead to a reduction in theoverall performance and responsiveness of the thermal sensor array.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention, which provides a system and a method fordetecting and imaging radiation.

In accordance with a preferred embodiment of the present invention, aradiation sensor is provided. The radiation sensor includes a substratewith electronic circuitry to detect changes in a transduction signal, anintermediate conductive layer above and electrically connected to theelectronic circuitry, and a lower separation layer with a highcoefficient of thermal resistance partially separating the intermediateconductive layer from the electronic circuitry. The radiation sensoralso includes a top layer above the intermediate conductive layer and anabsorptive layer over the top layer and electrically connected to theintermediate conductive layer. The absorptive layer produces thetransduction signal that is proportional to an amount of radiationincident on the absorptive layer.

In accordance with another preferred embodiment of the presentinvention, a micro electromechanical system is provided. The microelectromechanical system includes a substrate including electroniccircuitry to detect changes in transduction signals and an array ofradiation sensors. Each radiation sensor includes an intermediateconductive layer above and electrically connected to the electroniccircuitry, and a lower separation layer with a high coefficient ofthermal resistance partially separating the intermediate conductivelayer from the electronic circuitry. Each radiation sensor also includesa top layer above the intermediate conductive layer and an absorptivelayer over the top layer and electrically connected to the intermediateconductive layer. The absorptive layer produces the transduction signalthat is proportional to an amount of radiation incident on theabsorptive layer.

In accordance with another preferred embodiment of the presentinvention, a method for forming a thermal sensor is provided. The methodincludes depositing an insulating a layer over a substrate, and openingcontacts in the insulating layer. The method also includes forming afirst spacer layer, forming an intermediate conductive layer over thefirst spacer layer and electrically connected to the substrate, andforming a second spacer layer over the intermediate conductive layer.The method further includes forming a top layer over the second spacerlayer, depositing a radiation absorptive layer over the top layer andelectrically connected to the intermediate conductive layer, andremoving the first spacer layer and the second spacer layer.

An advantage of a preferred embodiment of the present invention is thata thermal sensor array can be created with low thermal mass, which canimprove the response time of the thermal sensor array. The improvedresponse time can yield better radiation detection and imagingperformance.

A further advantage of a preferred embodiment of the present inventionis that a thermal sensor array can be created with a high fill factor.The thermal sensor array with a high fill factor can have a bettersignal-to-noise ratio than thermal sensor arrays with a low fill factor.

Yet another advantage of a preferred embodiment of the present inventionis that the manufacture of the thermal sensor array can be performedusing existing manufacturing technology, therefore, the manufacture ofthe thermal sensor arrays can be achieved with a small investment infabrication facilities.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 a and 1 b are diagrams of prior art thermal sensor pixels;

FIGS. 2 a through 2 d are diagrams of different views of a pixel of athermal sensor array, according to a preferred embodiment of the presentinvention;

FIGS. 3 a through 3 d are diagrams of different views of a pixel of athermal sensor array, according to a preferred embodiment of the presentinvention;

FIG. 4 is a diagram of a pixel of a thermal sensor array, according to apreferred embodiment of the present invention;

FIGS. 5 a through 5 k are diagrams of the fabrication of a pixel of athermal sensor array, according to a preferred embodiment of the presentinvention;

FIGS. 6 a through 6 d are diagrams of the fabrication of a pixel of athermal sensor array, according to a preferred embodiment of the presentinvention; and

FIGS. 7 a and 7 b are diagrams of the fabrication of a pixel of athermal sensor array, according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely a high fill factor thermalsensor array with a low thermal mass and fast response time. The size ofeach thermal sensor pixel in the thermal sensor array can be scaledwithout incurring dramatic increases in cost or manufacturingdifficulty. These thermal sensor arrays may be referred to as microelectromechanical systems.

With reference now to FIGS. 2 a through 2 d, there are shown diagramsillustrating a cross-sectional view of a single pixel of a thermalsensor array and top views of different layers of the single pixel,according to a preferred embodiment of the present invention. Thediagram shown in FIG. 2 a illustrates a first layer 205 of a singlepixel of a thermal sensor array. The first layer 205 comprises a blanketoxide layer that can be used to cover a substrate (not shown in FIG. 2a) that includes necessary electronics to detect changes in transductionsignals, such as changes in resistance or voltage. The first layer 205can include vias 210 to allow for electrical contact with electrodes inthe substrate underneath the first layer 205. According to a preferredembodiment of the present invention, at least two vias 210 are needed inthe first layer 205.

The diagram shown in FIG. 2 b illustrates a second layer 215. The secondlayer 215 can be a metallic structure that is formed from aluminum or analloy of aluminum, for example. Additionally, other materials that havean appreciable coefficient of thermal resistivity, such as vanadiumoxide (VOx) can be used to form the second layer 215. The second layer215 is separated from the first layer 205 by a layer of vacuum, air, orsome other type of gas, with the vacuum, air, or gas providing thermalisolation for the second layer 215. The second layer 215 comprises aserpentine 220 and a center mass 222. The serpentine 220 and the centermass 222 can be electrically connected to the electronics in thesubstrate with vias 225, while anchor vias 230 physically connect theserpentine 220 and the center mass 222 to the first layer 205 (the oxidelayer). The serpentines 220 electrically couple the center mass 222 tothe electronics in the substrate, with the long circuitous routing ofthe serpentines 220 providing a measure of thermal isolation. Althoughshown in FIG. 2 b as being located in approximately the center of thesecond layer 215, the center mass 222 may actually be located at otherparts of the second layer 215.

The diagram shown in FIG. 2 c illustrates a third layer 235. The thirdlayer 235 can be a metallic structure or a multilayer stack formed froma metal and some other material. The metallic structure or themultilayer stack can be formed over the second layer 215 and isseparated from the second layer 215 by a layer of vacuum, air, or someother type of gas. Again, the layer of vacuum, air, or gas providesthermal isolation from the second layer 215. Alternatively, the thirdlayer 235 can be formed from a non-metallic material, with the onlyrequirement being that the material used being capable of thermallyconductive. The third layer 235 includes vias 240 that permit theconnection of the third layer 235 to the second layer 215. The thirdlayer 235 can then be covered by a radiation (for example, infraredradiation) absorbing material. Alternatively, the multilayer stackforming the third layer 235 can include a layer of the radiationabsorbing material, typically on a top layer.

The diagram shown in FIG. 2 d illustrates a cross-sectional view of aportion of the single pixel of the thermal sensor array. The singlepixel of the thermal sensor array includes the first layer 205 formedover electronics, which can include a metal contact 250, that willpermit electrical connectivity of the first layer 215 to the electronicsby way of the via 225. The metal contact 250 may be formed over asubstrate 255. The second layer 215 may also be connected to the firstlayer 205 by the anchor via 230. The connection between the second layer215 and the metal contact 250 by the via 225 can be electrical innature, while the connection between the second layer 215 and the firstlayer 205 by the via 230 is a physical connection. The third layer 235can be connected to the second layer by the via 240. Also shown in thediagram are the layers of vacuum, air, or some other type of gasseparating the second layer 215 from the first layer 205 and the thirdlayer 235 from the second layer 215.

With reference now to FIGS. 3 a through 3 d, there are shown diagramsillustrating a cross-sectional view of a single pixel of a thermalsensor array and top views of different layers of the single pixel,according to a preferred embodiment of the present invention. Thediagrams shown in FIGS. 3 a through 3 d illustrate an alternateembodiment of the present invention, wherein the first layer 205includes vias 305 that allow vias 230 in the second layer 215 to makecontact with metal contacts 310 and 311 present in the substrate 315.According to a preferred embodiment of the present invention, the metalcontacts 310 can be used to provide electrical connectivity, while metalcontacts 311 are electrically isolated, functioning only to provide asolid physical connection. The connection offered by the vias 230 andthe vias 305 to the metal contacts in the substrate provides a strongphysical connection between the second layer 215 and the substrate 315.Furthermore, the connection to the substrate 315 can allow for betterthermal conductivity and therefore a shorter sensor response time.

With reference now to FIG. 4, there is shown a diagram illustrating across-sectional view of a single pixel of a thermal sensor array,according to a preferred embodiment of the present invention. Thediagram illustrates a cross-sectional view of an alternate embodiment ofa single pixel of a thermal sensor array, wherein the second layer 215is a multi-layer stack, with a first stack layer 405 formed from anoxide and a second stack layer 410 formed from a material with a largecoefficient of thermal resistance, such as vanadium oxide (VOx),aluminum (Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), aswell as semiconductors and semiconductor alloys, such as silicongermanium (SiGe), protein thin films, such as cytochrom C, and so forth.Vias 415 and 420 in the second layer 215 can be specially formed so thatthe portion of the first stack layer 405 at the bottom of the vias 415and 420 are removed (such as by etching) so that the second stack layer410 can make physical contact with the first layer 205 (via 415) or themetal contact 250 (via 420). The contact between the second stack layer410 and the first layer 205 and the metal contact 250 permitted by thevias 415 and 420 affords an increase in the thermal isolationcharacteristics of the thermal sensor array.

The third layer 235 can also be a multi-layer stack, with a first stacklayer 425 formed from a metallic material, such as aluminum or an alloyof aluminum, and a second stack layer 430 formed from a radiationabsorbing material, such as mesoporous metals, an optical interferencestack, and so forth. Vias, such as via 435, permit the third layer 235to attach to the second layer 215. The connection between the thirdlayer 235 and the second layer 215 provided by the via 435 can be both aphysical connection and an electrical connection.

According to a preferred embodiment of the present invention, the secondstack layer 430 (or a top portion of a single layered third layer) canbe formed using deposition techniques in a partial pressure of an inertgas, such as argon. The presence of argon can diminish the atomistickinetic energy of many materials to a point where when the atoms (ormolecules) of the materials strike the surface (such as the first stacklayer 420 or a bottom portion of a single layered third layer), a highlyroughened web-like surface is created. This roughened surface can helpto decrease reflectivity in the electromagnetic band of interest, forexample, IR.

With reference now to FIGS. 5 a through 5 k, there are shown diagramsillustrating cross-sectional views of a single pixel of a thermal sensorarray during the fabrication of the thermal sensor array, according to apreferred embodiment of the present invention. The diagram shown in FIG.5 a illustrates a substrate 505. The substrate 505 may already containelectronics previously fabricated, but not shown. The electronics can beused in the detection of changes in transduction signals, providinginformation regarding changes in resistance and voltage, for example.The substrate 505 may also include metal contacts (also not shown) thatwill allow electrical connectivity between the electronics alreadyfabricated in the substrate 505 and the pixel of the thermal sensorarray to be fabricated.

The diagram shown in FIG. 5 b illustrates an oxide layer 510 depositedover the substrate 505. The oxide layer 510 can function as anelectrical insulator as well as a thermal insulator. The diagram shownin FIG. 5 c illustrates a via 512 formed in the oxide layer 510. Afterthe deposition of the oxide layer 510, vias, such as the via 512, can becreated in the oxide layer 510 to permit electrical connectivity and/orphysical connectivity to the substrate 505. The oxide layer 510 can beetched using typical etching techniques, such as those employing aresist layer (not shown) that is patterned and then developed andfollowed by an etch. After the oxide layer 510 has been etched, theresist layer can be stripped.

The diagram shown in FIG. 5 d illustrates a resist layer 515 depositedover the oxide layer 510, using spin coat techniques, for example. Theresist layer 515 can function as a spacer layer to permit the formationof elevated structures, such as the second layer 215 (FIG. 2 d), forexample. After the formation of the elevated structures, the resistlayer 515 and other similar layers can be removed to free the elevatedstructures to move (for use in micro electromechanical systems (MEMS)),thermally isolate the elevated structures (for use in thermal sensors),and so forth. The resist layer 515 can also be patterned to create vias.The diagram shown in FIG. 5 e illustrates vias 517 and 519 created inthe resist layer 515. The patterning of the resist layer 515 can beperformed using typical techniques, such as by exposing the resist layer515 with a desired pattern and then developing the resist layer 515 toremove portions of the resist layer 515. The via 517 is located at aposition so that it opens the resist layer 515 all the way to thesubstrate 505, while the via 519 is located so that it opens the resistlayer 515 to the oxide layer 510.

After the patterning of the resist layer 515, a middle conductor layer520 can be deposited, shown in FIG. 5 f. Deposition of the middleconductor layer 520 can be performed using standard techniques, such assputter deposition. The middle conductor layer 520 may be formed from ametallic material such as aluminum or an alloy of aluminum.Alternatively, the middle conductor layer 520 may be a multi-layer stack(such as shown in FIG. 4, the first stack layer 405 and the second stacklayer 410, for example). Although the discussion focuses on the middleconduction layer 520 being formed from a metallic material, othermaterials can be used, such as oxides, materials with large coefficientsof thermal resistivity (for example, vanadium oxide), and so forth.

The middle conductor layer 520 can then be patterned, to create anopening or a serpentine pattern (such as the serpentine 220 (FIG. 2 b)),as shown in FIG. 5 g. For example, an opening 522 can be patterned intothe middle conductor layer 520. The patterning of the middle conductorlayer 520 can be performed using typical methods, such as with the useof a resist layer that can be patterned and then developed, followed byan etching of the middle conductor layer 520 and then a strip of theresist layer. After the patterning of the middle conductor layer 520, asecond resist layer 525 can be deposited (as shown in FIG. 5 h). Thesecond resist layer 525 can be functionally equivalent to the resistlayer 515 and permit the formation of elevated structures, such as thethird layer 235 (FIG. 2 d), for example.

As with the resist layer 515, the second resist layer 525 can bepatterned to create vias, as shown in FIG. 5 i. A via 527 can bepatterned into the second resist layer 525, with the patterning usingtypical techniques, such as exposing the second resist layer 525 with adesired pattern and then developing the second resist layer 525 toremove portions of the second resist layer 525. After the second resistlayer 525 is patterned, an upper layer 530 can be formed (shown in FIG.5 j). After the formation of the upper layer 530, an absorptive layer535 can be formed over the upper layer 530, such as by depositiontechniques. Alternatively, the upper layer 530 can be formed from anabsorptive material, thereby eliminating the need for a multi-layeredtop layer. After the fabrication of the top layer (the upper layer 530and the absorptive layer 535 or simply the upper layer 530) is complete,the resist layer 515 and the second resist layer 525 can be removed, asshown in FIG. 5 k. The removal of the resist layer 515 and the secondresist layer 525 can be achieved using an isotropic etch, for example.

With reference now to FIGS. 6 a through 6 d, there are shown diagramsillustrating cross-sectional views of a single pixel of a thermal sensorarray during the fabrication of the thermal sensor array, according to apreferred embodiment of the present invention. The diagrams shown inFIGS. 6 a through 6 d illustrate an alternate embodiment of the presentinvention, wherein the bottoms of vias are removed to help improve thecoefficient of thermal resistance of the thermal sensor array. Thediagrams shown in the figures can occur as a replacement or anenhancement to deposition of the middle conductor layer 520 (FIG. 5 f).

Rather than covering the resist layer 515 with a metallic material toform the middle conductor layer 520, an oxide layer 605 is used to coverthe resist layer 515 (FIG. 6 a), which can be followed with theformation of an auxiliary resist layer 610 (FIG. 6 b), with theauxiliary resist layer 610 covering the oxide layer 605. The auxiliaryresist layer 610 can be patterned and developed to create vias, such asvia 615 (FIG. 6 b). An etching operation can be used to remove a portionof the oxide layer 605 exposed by the via 615 in the auxiliary resistlayer 610 (FIG. 6 c). The removal of the portion of the oxide layer 605exposes the substrate 505. The auxiliary resist layer 610 can then beremoved (stripped) as shown in FIG. 6 d and the fabrication of thethermal sensor array can then continue, with the continued fabricationof the middle conductor layer 520, such as with a deposition of amaterial with a high coefficient of thermal resistance.

With reference now to FIGS. 7 a and 7 b, there are shown diagramsillustrating cross-sectional views of a single pixel of a thermal sensorarray undergoing fabrication, according to a preferred embodiment of thepresent invention. The diagrams shown in FIGS. 7 a and 7 b illustrate analternate embodiment of the present invention, wherein the bottoms ofvias are removed to help improve the coefficient of thermal resistanceof the thermal sensor array. The diagrams shown in the figures can occuras a replacement or an enhancement to deposition of the middle conductorlayer 520 (FIG. 5 f).

As discussed above, rather than covering the resist layer 515 with ametallic material to form the middle conductor layer, an oxide layer 705can be used to cover the resist layer 515 (FIG. 7 a). The oxide layer705 follows the pattern of the resist layer 515 and can form vias 710and 715. This can be followed with an oxide etch to clear the viabottoms and expose the substrate 505 and the oxide layer 510. Thefabrication of the thermal sensor array can then continue, with thecontinued fabrication of the middle conductor layer 520, such as with adeposition of a material with a high coefficient of thermal resistance.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A radiation sensor comprising: a substrate having electroniccircuitry to detect changes in a transduction signal; an intermediateconductive layer disposed above and electrically connected to theelectronic circuitry; a lower separation layer having a high coefficientof thermal resistance partially separating the intermediate conductivelayer from the electronic circuitry; a top layer disposed above theintermediate conductive layer, wherein the intermediate conductive layercomprises two thin conductive elements having thin serpentine patternsand electrically coupling the top layer to the electronic circuitry; andan absorptive layer overlying the top layer and electrically connectedto the intermediate conductive layer, wherein the absorptive layerproduces the transduction signal that is proportional to an amount ofradiation incident on the absorptive layer.
 2. The radiation sensor ofclaim 1, wherein the top layer is partially separated from theintermediate conductive layer by an upper separation layer having a highcoefficient of thermal resistance.
 3. The radiation sensor of claim 1,wherein the lower separation layer having a high coefficient of thermalresistance is selected from the group consisting of: air, a vacuum, agas, and combinations thereof.
 4. The radiation sensor of claim 1further comprising an insulating layer formed between the electroniccircuitry and the lower separation layer, the insulating layer havingopenings to permit electrical connections between the electroniccircuitry and the intermediate conductive layer.
 5. The radiation sensorof claim 4, wherein the insulating layer comprises an oxide.
 6. Theradiation sensor of claim 1, wherein the intermediate conductive layeris separated from the top layer by a second separation layer having ahigh coefficient of thermal resistance.
 7. The radiation sensor of claim1, wherein the intermediate conductive layer is coupled to theelectronic circuitry by two electrical contacts, and wherein theintermediate conductive layer is coupled to the top layer at a mass, andwherein each of the two thin conductive elements uniquely couples arespective one of the two electrical contacts to the mass.
 8. Theradiation sensor of claim 1, wherein the thin conductive elements have alarge coefficient of thermal resistivity.
 9. The radiation sensor ofclaim 1, wherein the thin conductive elements comprise a materialselected from the group consisting of: vanadium oxide (VOx), aluminum(Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), silicongermanium (SiGe), cytochrom C, and combinations thereof.
 10. Theradiation sensor of claim 1, wherein the thin conductive elements arephysically anchored to an insulating layer positioned between theelectronic circuitry and the intermediate conductive layer to maintainstability.
 11. The radiation sensor of claim 1, wherein the intermediateconductive layer comprises: an oxide layer; a layer having a largecoefficient of thermal resistance disposed over the oxide layer; andcontact points physically connecting the intermediate conductive layerand the electronic circuitry.
 12. The radiation sensor of claim 1,wherein the radiation is infrared radiation.
 13. A microelectromechanical system comprising: a substrate comprising electroniccircuitry to detect changes in transduction signals; and an array ofradiation sensors, each radiation sensor comprising an insulating layerdisposed above the electronic circuitry; an intermediate conductivelayer disposed above the insulating layer and electrically connected tothe electronic circuitry; a lower separation layer having a highcoefficient of thermal resistance partially separating the intermediateconductive layer from the electronic circuitry; a top layer disposedabove the intermediate conductive layer, wherein the intermediateconductive layer comprises two thin conductive elements having thinserpentine patterns and electrically coupling the top layer to theelectronic circuitry; and an absorptive layer overlying the top layerand electrically connected to the intermediate conductive layer, whereinthe absorptive layer produces one of the transduction signals that isproportional to an amount of radiation incident on the absorptive layer.14. The micro electromechanical system of claim 13, wherein the microelectromechanical system is vacuum sealed in a package.
 15. The microelectromechanical system of claim 13, wherein the electronic circuitryproduces electrical signals based on radiation incident on the array ofradiation sensors.
 16. A method for forming a thermal sensor, the methodcomprising: depositing an insulating layer over a substrate; openingcontacts in the insulating layer; forming a first spacer layer; formingan intermediate conductive layer comprising two thin conductive elementshaving thin serpentine patterns over the first spacer layer andelectrically connected to the substrate; forming a second spacer layerover the intermediate conductive layer; forming a top layer over thesecond spacer layer and electrically connected to the two thinconductive elements of the intermediate conductive layer; depositing aradiation absorptive layer over the top layer; and removing the firstspacer layer and the second spacer layer.
 17. The method of claim 16,wherein the forming the intermediate conductive layer comprises:depositing the intermediate conductive layer; and patterning theintermediate conductive layer.
 18. The method of claim 17, wherein theintermediate conductive layer comprises an oxide layer, and wherein theforming the intermediate conductive layer comprises etching awayportions of the intermediate conductive layer to form via bottoms. 19.The method of claim 17, wherein the intermediate conductive layercomprises an oxide layer, and wherein the forming the intermediateconductive layer comprises: depositing a resist layer; developing theresist layer; etching away portions of the intermediate conductivelayer; and stripping the resist layer.
 20. The method of claim 16,wherein the absorptive layer is formed by deposition in the presence ofan inert gas.